This seems to work in both Firefox and Internet Explorer.  Basically it generates a form with hidden fields. You could change the method to post or get.  You could also change any of the fields and the form action depending on what form you are trying to automatically submit.  I reccomend you put a friendly button value incase they are in a browser with javascript disabled.  Then a little javascript snippet automatically submits the form.

{codecitation class="brush:html"}

 <center>
<form name="myForm" action="http://www.google.com/search" method="get">
<input name="q" type="hidden" value="baseball" />
<input name="save" type="submit" value="Click Here To Do A Google Search For Baseball" />
</form></center>   
<script language="javascript">document.myForm.submit();</script>

{/codecitation}